Magnetic fields and massive star formation Qizhou Zhang Harvard-Smithsonian Center for Astrophysics
Role of Magnetic Field in Star Formation Cloud scale: formation/support magnetic or turbulent? Clump Scale: What controls clump fragmentation and core formation? Does massiesf proceed in equilibrium? Core disk Scale: Magnetic braking - remove angular momentum? NGC1333 IRAS4A Girart et al. 2006 Chapman et al. 2010 See review by McKee & Ostriker 2007 Crutcher 2012 B field direction 870 µm Cont.
Techniques to Measure B-fields Zeeman Splitting: B los, limited by sensitivity unless for masers. Linear polarization caused by aligned aspherical dust grains in presence of B fields (Emission: Pol B; Absorption: Pol B): Measure morphology only, infer B pos Goldreich & Kylafis effect See Review by Crutcher 2012, Lazarian 2007
Magnetic field morphology from dust polarization Diagnostic tools: Comparing magnetic field orientation (Bpos) at different spatial scales Comparing Bpos orientation with respect to cloud morphology Using dispersion of Bpos orientation à B
Magneto hydrodynamic simulation with turbulence: Sheets Gas collapse along field lines to form dense filaments B Diffuse and lower density gas B β = P th /P B = 1/24, Strong B field B Nakamura & Li (2008) See also Nagai et al. 1998; Soler et al. 2013; van Loo et al. 2014
NGC 6334: Magnetic fields from GMC to cores Magetic field orientation maintained from 100pc to 0.1 pc Li et al. 2015 See also Zhang et al. 2014
Massive Filaments in G14.2 Busquet, Zhang et al. 2012 Cloud size ~ 8 pc 74 clumps Masses:11-1000 M Clump sizes: 0.2-1.2 pc VLA NH 3 on Spitzer 8 µm
Massive Filaments in G14.2 2 M vir 5σ R α = = M GM B = 0.3-0.5 mg Bonnor Ebert Sphere α = 2 α decreases with spatial scales Non equilibrium SF? What about support from B fields? Ohashi+ 2016, in prep Busquet+ 13; Santos+ 2015 B field from IR Santos+ 2016 See also Pillai+ 2015
Cores contain many Jeans mass (Case study G28.34) n(h 2 )=7x10 4 cm -3, T=15K M J (thermal) = 2 Msun L J = 0.1 pc è For spatially resolved cores (res < L J ) M core /M J > 10, 2 3/ 2 J = ρo π πc 6 G 38 Msun s 1/ 2 M 3 4.3pc 0.1 pc σv=0.7 km/s M turb_j ~ 30 Msun L turb_j ~ 0.3 pc 22 Msun Turbulence (and B field ) supported fragmentation? Zhang, Wang, Pillai, Rathborne 2009 See also Brogan et al. 2009; Longmore et al 2010; Csengeri et al. 2010, 11; Pillai et al. 2011; Tan et al. 2013, WagnApri et al. 6-9, 2011, 20162012, 2014
Is cluster forming region G28 in equilibrium 2 M vir 5σ R α = = M GM Zhang et al. 2009; 2015; Zhang et al. 2015
NH3 Core properties in 67 massive young stellar objects Many Cores are sub-virial: Mvir/M < 1 Lu et al. 2014 distribution of the virial parameter See also Pillai+ 2011, Kauffmann+ 2013
SMA Polarization Legacy Survey 21 massive molecular clumps, largest by (sub)mm interferometer Subcompact/compact/extended configurations à 1-3 Goal: To obtain data for a large sample of massive molecular clumps to investigate the role of magnetic fields in fragmentation of massive molecular clumps and formation of cores through imaging of dust/co polarization, and kinematics of molecular gas. PI: Qizhou Zhang Co-Is: Keping Qiu, Ya-Wen Tang, Hau-Yu Liu, How-Huan Chen, Josep Girart, Ramprasad Rao, Paul Ho, Patrick Koch, Shih-Ping Lai, Hue-Ru Chen, Eric Keto, Zhi-Yun Li, Tao-Chung Ching Sylvain Bontemps, Timea Csengeri, Huabai Li, Pau Frau, Marco Padovani Summary paper: Zhang, Q., Qiu, K., Girart, J. M., et al. 2014, ApJ, 792, 116 Detailed analysis: Girart, J. M., Frau, P., Zhang, Q., et al. 2013, ApJ, 772, 69 Koch, P. M., Tang, Y.-W., Ho, P. T. P., et al. 2014, ApJ, 797, 99 Li, H. et al. 2015, Nature, 520, 518 Liu, H. B., Qiu, K., Zhang, Q., Girart, J. M., & Ho, P. T. P. 2013, ApJ, 771, 71 Qiu, K., Zhang, Q., Menten, K. M., Liu, H. B., & Tang, Y.-W. 2013, ApJ, 779, 182 Qiu, K., Zhang, Q., Menten, K. M., et al. 2014, ApJ, 794, L18
G240: Dust Polarization and Outflow B Field B = 1.2 mg, β = 0.4, M/Flux = 1.1 G240.31 (10 4.7 L ): Qiu et al. 2009, 2014 See also Girart, Beltran, Zhang, Rao, Estalella 2009 Lai et al. 2003; Rao et al. 1998; Cortes et al. 2000; Tang et al. 2008, 2009,2012; Kock 2012; Hull et al. 2013. Sridharan et al. 2013 Single Dish: Matthews et al. 2009; Dotson et al. 2010
Polarization Maps
DR21 Filament in Cygnus X 0.8mm continuum and B field direction CSO SMA: DR 21(OH) 0.4pc 4pc Girart et al. 2013 Kirby et al. 2009 Hennemann et al. 2012
B field in core scales versus B field in clump Two groups of cores: One group with B core B clump, Other group B core B clump. > 60% of small scale B follow direciton of B clump. The bi-modal distribution suggests that B fields are dynamically important during the collapse of pc-scale clumps and the formation of 0.1pc dense cores. Simulation: B-fields aligned within a 35º cone B core B clump Random B core B clump Simulation: B-fields aligned within a 80-90º Zhang et al. 2014
Why there is a peak at 90d? From the lower density gas draged along the large scale magnetic field lines? (sample is too small to tell). Angular momentum (rotation) at core scales drags the field, rendering it perpendicular to the large scale field? (There is a hint in the data, and should be investigated further) Sample studied is still small, the peak at 90d might be caused by few objects.
B field in cores versus outflows Small # of statistics, but there appears to be no preferred alignment à Angular momentum dominates B field at 10 3 AU scale? Or gas and B decoupled in dense regions? B Core Outflow Axis B Core Outflow axis
Conclusions Recent polarization data of statistically significant samples found magnetic fields are correlated in scales from clumps (1pc) à cores (0.01-0.1pc). Statistical analysis finds 1-10 mg in clumps and cores. These findings indicate magnetic fields are dynamically important at these scales and play a dynamically important role in massive star formation. Magnetic fields in dense cores do not correlate with outflow axis, suggesting that in (peudo)disk scales, angular momentum dominates over magnetic fields.